Lock devices and key devices are evolving from the traditional pure mechanical locks. These days, there are wireless interfaces for electronic lock devices, e.g. by interacting with a portable key device. For instance, Radio Frequency Identification (RFID) has been used as the wireless interface. When RFID is used, the user needs to present the portable key device very close to a reader of the lock. However, in order to provide a more user friendly solution, wireless interfaces with greater range are starting to be used. This allows the interaction between the portable key device and the lock to occur without user interaction, e.g. with a portable key device being located in a pocket or handbag. However, in such a situation, there is a risk that someone on the inside unlocks the lock device by simply walking by the lock device. In order to prevent this from happening, without introducing user interaction to open the lock device, there needs to be a way to determine whether a portable key device is on the inside or on the outside.
US 2013/0176107 presents a wireless access control system includes a remote access device and an electronic lock. The electronic lock communicates with the remote access device. The electronic lock controls the ability to lock and unlock a door in which the electronic lock is disposed. The electronic lock determines when the remote access device is at a distance less than or equal to a predetermined distance from the lock to enable the lock to be unlocked. More specifically, an internal antenna and an external antenna are used to determine which side the user is on. If a calibrated RSSI from the internal antenna is greater than the RSSI reading or readings from external antenna, user is determined to be on the inside.
However, such a determination of position based on dual antenna RSSI is not always ideal. In some circumstances, radio signals are distorted by reflections and fading which depends on external objects and interference, which can not be reliably controlled.